Several hydroperoxides have important uses in various chemical processes. For example, ethylbenzene hydroperoxide and t-butyl hydroperoxide are used in the epoxidation of propylene to form propylene oxide. When propylene epoxidation is carried out with ethylbenzene hydroperoxide, styrene is also formed as a co-product. The cleavage of cumene hydroperoxide leads to the formation of phenol and acetone.
The hydroperoxides may be prepared by free radical chain reactions wherein the base compound, e.g., cumene, is oxidized with air or oxygen to form the corresponding hydroperoxide. To increase conversion efficiency catalysts and promoters are generally utilized. Various modifications of this common process for the production of hydroperoxides are disclosed in the art.
The starting material for hydroperoxide formation typically is an organic compound, which may be substituted or unsubstituted, having at least one secondary or tertiary hydrogen. Compounds having tertiary hydrogens are more readily oxidized to the hydroperoxide.
Illustrative of processes for the production of cumene hydroperoxide is the method disclosed in U.S. Pat. No. 2,577,768 (1951). Cumene is oxidized to the corresponding hydroperoxide by bubbling air into a mixture of cumene and NaHCO.sub.3 which is used as a catalyst. The reaction is carried out at 75.degree. C. A 26% conversion after 72 hours is alleged.
The use of heavy metal catalysts to improve conversion efficiencies is disclosed in British Pat. No. 665,897. The catalyst is a compound of Mn, V, Co, Pb, Ni, Fe, Cu, Cr or Hg. The preferred compounds are the oxides, hydroxides or organic acid salts which are soluble in the organic compound to be oxidized, e.g, cumene. Conversion of 58% at 45.degree. C. is alleged.
Other catalysts disclosed in the art for alkyl hydroperoxide production include CaCO.sub.3 (U.S. Pat. No. 2,913,277), phthalorganic salts (British No. 801,347), ethylenediamine tetraacetic acid (U.S. Pat. No. 2,861,107) and arylisobutyronitrile (Ger. offen. No. 2,035,504).
The use of elevated temperatures to produce hydroperoxides is often disadvantageous since side reactions may occur and the hydroperoxide is decomposed. Picoline, pyrrole or thiophene are disclosed as side reaction inhibitors. See Japanese Pat. No. 58045. Similarly the art teaches that copper, silver and gold will act as inhibitors for that decomposition. See, for example, U.S. Pat. No. 2,820,832.
A typical method for the preparation of ethylbenzene hydroperoxide is disclosed in U.S. Pat. No. 2,749,368. The process is similar to that for cumene hydroperoxide formation. Copper is utilized as a catalyst and the reaction temperature is about 50.degree. C. below the boiling temperature of the hydrocarbon being oxidized. Other related processes are alkali metal carbonates, bicarbonates and oxides as catalysts for the preparation of ethylbenzene hydroperoxide; see U.S. Pat. No. 2,367,666.
Tertiary butyl hydroperoxide is of considerable commercial importance and is widely used as a free-radical initiator for polymerization processes. It can be prepared non-catalytically by the auto oxidation of isobutane at about 100.degree. C. to about 150.degree. C. in a metal ion free reaction medium at a pressure of about 400 psig; see U.S. Pat. No. 2,845,461. The catalysts which are disclosed as being useful in the preparation of cumene hydroperoxide and ethylbenzene hydroperoxide may be advantageously utilized in the preparation of t-butyl hydroperoxide.
There have been various attempts to avoid the use of elevated temperatures by utilizing free radical initiators other than heat, e.g., radiation and photon sources. For example, U.S. Pat. No. 3,113,085 (1963) discloses that conversion rates of 26% can be achieved in the production of cumene hydroperoxide at a dose rate of 100 rad/min. The temperature is maintained below 70.degree. C., the decomposition temperature of the hydroperoxide.
French Pat. No. 1,239,348 (1960) discloses the photo oxidation of cumene to cumene hydroperoxide utilizing a mercury vapor lamp as the photon source and benzophenone as a photochemical sensitizer. Similarly, U.S. Pat. No. 2,973,310 discloses the use of an ultra violet (UV) light source in conjunction with a free radical initiator, e.g., Ba(OH).sub.2. Titanium dioxide is disclosed as a suitable catalyst for the photo oxidation of cumene using a UV source of about 3000-4000 .ANG. wavelengths. The reaction is carried out at 25.degree. C. to 130.degree. C.; see U.S. Pat. No. 2,955,996 (1960).
Recently, the use of lasers to produce hydroperoxides from cumene was described in an article by R. B. Hall, "Laser In Industrial Chemical Synthesis", September, 1982, Laser Focus, pp. 57-62. The disclosure is of the work of the instant inventors.
In a similar vein, there exist a number of publications suggesting various accelerators in the oxidation of hydrocarbons to their hydroperoxide analogs.
The process shown in U.S. Pat. No. 2,674,629, issued Apr. 6, 1954, to Scriabine, begins with cumene or "other aliphatic-aromatic hydrocarbons" and prepares hydroperoxides of those beginning compounds by subjecting the feed material to treatment in the liquid phase with oxygen at an elevated temperature in the presence of a .beta.-ketonic ester. The ester preferably is ethyl acetoacetate or ethyl benzoylacetate.
Similarly, the process in U.S. Pat. No. 2,792,424, issued May 14, 1957, to Weesner synthesizes various hydroperoxides of cumene, ethylbenzene, diphenylmethane and the like at high temperatures in liquid phase using oxygen and a .beta.-diketone which is free from ester groups in a position which is beta to the keto group. The preferred initiator apparently is 2,4-pentanedione.
In U.S. Pat. No. 2,797,425, issued May 14, 1957 also to Werner, the oxidation initiators disclosed are the esters of malonic acid or of substituted malonic acid. The preferred class includes those malonic esters which has at least one hydrogen atom on the carbon atom joining the two ester or carboalkoxy groups. The apparently preferred initiators are diethyl malonate or diethyl (isobutyl) malonate.
In Kulicki et al, Rocz. Chem. 1971, 45(4), pp. 601-6, the effect of the accelerators acetophenone and dimethylphenylcarbinol on the 1,1-azobis-(1-cyclohexanenitrile) initiated or cumene hydroperoxide initiated oxidation of cumene to cumene hydroperoxide was studied. Both accelerators were said to promote the cumene hyperoxide initiated reaction although the effect of dimethylphenylcarbinol was more pronounced.
None of these publications show the use of a ketone as a promoter in the liquid phase reaction of hydrocarbons to the hydroperoxide form and wherein the promoter activity of the ketone is greater than acetophenone.